Positive drive belts (also called interchangeably “synchronous” or “timing” belts) are well known and in common usage. Such belts are generally made of a resilient elastomer and are reinforced with a longitudinal tensile member that lies along the pitch line of the belt and is made up of a plurality of cords of a high elastic modulus. The cords may be made from glass, steel, aramid or carbon fiber in order to support the tensile loads in the belt. The belt includes spaced-apart teeth formed of neoprene, HNBR, urethane, polychloroprene, polyurethane, NBR, or other thermoset or thermoplastic elastomers available to the industry. The tooth surface may be reinforced with an abrasion resistant fabric such as nylon that resists abrasion and helps resist shearing off of the tooth from the cord under load.
While working well, belts of the conventional construction described above remain susceptible to damage or tooth breakage from shear forces when subjected to high loads as part of a duty cycle or during misuse. Conventional belts that rely on the face fabric of the belt as a means for reinforcing the belt teeth have proven ineffective. Such designs ultimately depend on adhesion of the elastomer to the cord and face fabric and on the shear strength of the elastomer. The face fabric structure cannot compensate for a failure of the adhesive or elastomer. Adding additional layers of fabric in the tooth region for the purpose of reinforcement adds to the cost of the belt. In addition, a belt tooth which has become detached from the tensile cord is often still loosely attached to an adjacent tooth by the detached face fabric and can move to positions that prevent proper engagement of the remaining belt teeth to the pulley teeth.
As a result, the industry remains in need of a belt configuration that is resistant to tooth shear. Optimally, the belt will be resistant to tooth shear failure and also have a soft mode of failure wherein the teeth remain loosely attached to the cord in a position that permits belt operation even if cracked or sheared off. Such a belt should further resist tooth shear damage resulting from temporary high loads that can occur during part of the duty cycle or during misuse. Still further, a belt configuration is needed within the industry that overcomes belt failure due to tooth shear in a cost effective, dependable manner.